The overall goal of this research is to develop a novel, non-invasive method for nerve conduction block that could be employed as a treatment for complications of neurological disorders, including spasticity and pain, using image-guided focused ultrasound. Focused ultrasound is a therapeutic modality that can be applied percutaneously to achieve focal heating and mechanical disruption of a small volume of internal tissue without damaging the intervening tissues. In preliminary studies, ultrasound-guided focused ultrasound treatment was effective in achieving complete conduction block of rabbit sciatic nerves, non-invasively; studies in rats showed that different treatment parameters led to variable effects on peripheral nerve conduction. To study such effects in more detail, the proposed research plan aims to test the following hypothesis: Ultrasound treatment of peripheral nerves will yield varying effects on nerve conduction that are dependent on the dose and frequency of ultrasound exposure. The effects most relevant to the treatment of conditions such as spasticity and pain primarily include: partial conduction block - incomplete suppression of nerve conduction (varying levels of suppression); and temporary conduction block - complete suppression of nerve conduction for a given duration that will recover over time. The research plan is to: Aim 1 - develop image-guided focused ultrasound devices to treat the rat sciatic nerve, non-invasively, and use electrophysiological, behavioral, and histological techniques to: Aim 2 - determine the optimal parameters of focused ultrasound to produce partial and temporary conduction blocks of nerves. Spasticity is prevalent as a complication of neurological disorders including spinal cord and brain injury and multiple sclerosis; pain affects many patients with similar injury, arthritis and cancer. It is our goal to develop image- guided focused ultrasound as a non-invasive alternative for the treatment of spasticity and pain.